1. Field of the Invention
The present invention relates generally to radiation detectors and, more particularly, to integrator circuitry and circuitry related thereto for providing a single channel circuit for a radiation detector.
2. Description of Related Art
Electronic circuits for radiation detectors have been utilized for over a century for the purpose of detecting pulses produced in a radiation sensor element as a result of impingement by some type of radiation. Presently, two channel radiation detection circuits are commonly utilized when it is desired to detect high energy and low energy pulses from the same radiation detector. The two channel radiation detection circuits require two separate circuits with different gains and threshold settings thereby requiring significant cost and reducing reliability. The inventors propose that it would be desirable to be able to process high energy and low energy pulses in a single channel.
Most modern radiation detectors depend on scintillation crystals, ion chambers, or semiconductor radiation detectors. Scintillation crystals respond to radiation by emitting a photon of light proportional to the energy of the charged particle that is stopped in the crystal. The most recent class of detector developed is the solid-state detector. These detectors convert the incident charged particles directly into electrical pulses. Solid-state detectors are fabricated from a variety of materials including: germanium, silicon, cadmium telluride, mercuric iodide, and cadmium zinc telluride. The best radiation detector for a given application will depend on the requirements of the application.
The input electronic circuits for related art radiation detectors are then designed around the type of radiation sensor utilized in the radiation detector. Therefore related art radiation detector circuitry is limited in flexibility of use with different radiation detectors. The inventors propose that it would be desirable to provide a universal detector circuit that may be utilized with many different types of detectors and require only a single channel for both high energy and low energy radiation events. Related art radiation detector circuitry are limited in various ways such as the two channel configuration and in other ways as discussed hereinafter that hinder or prevent this function.
In many cases, multiple radiation detectors are used simultaneously. Related art circuitry for multiple radiation detector systems not only tend to produce less accurate data, and require the more bulky two channel layout, but are also likely to miss data such as coincident detection of radiation particles from different radiation detectors. The related art designs require a computer or processor to poll, sample, and store data from multiple radiation detection circuit boards and thereby may provide limited data collection when multiple radiation events are detected in different detectors simultaneously or near simultaneously. Related art designs also require specialized connections that prevent reconfiguration of suites of radiation detectors.
The following patents disclose related art efforts related to the above-described and/or other problems and studies:
U.S. Pat. No. 4,078,178, issued Mar. 7, 1978, to Lowes, discloses a dynamic background subtraction circuit which improves the display resolution of radiation energy spectra, such as X-ray energy spectra in an X-ray energy spectrometer. In this circuit, the number of radiation events (counts) occurring at a reference or background energy level is subtracted from the number of radiation events (counts) occurring at a second energy level under study. The output of this circuit is a real-time (dynamic) approximation of the count rate at the energy level under study, but with resolution improved by subtraction of the background counts.
U.S. Pat. No. 4,217,497, issued Aug. 12, 1980, to Daniels et al, discloses a portable neutron spectrometer/kerma-rate meter for the measurement of the fast neutron component of mixed n-gamma fields in the 1 to 15 MeV neutron energy range. The system includes an organic scintillation detector, pulse shape discrimination circuitry, a 1.4 μs multichannel analyzer, an 8-bit microcomputer, and appropriate displays. The instrument is capable of both gathering and processing recoil-proton pulse-height data in the field.
U.S. Pat. No. 4,395,635, issued Jul. 26, 1983, to Friauf et al, discloses a gamma ray coincidence analysis system for a multichannel nuclear imaging device of the type employing scintillation detectors in ring-like arrays, with the detectors arranged in quadrants of the rings. The scintillation detectors in a ring have output circuits including respective timing discriminators and OR gates, and respective energy discriminators providing delayed energy pulses, and wherein timing pulses from the respective quadrants are fed via the OR gates to the inputs of a four-input coincidence detector without any delay except for a small delay internal to the discriminators and the very small delay of the OR gates. The delay of the energy pulses at the energy discriminators is for an energy validation period of 500 nsec. The output pulse from the coincidence detector is subsequently delayed for a similar period for verification of the energy levels of the two channels causing the coincidence. A data output signal is generated responsive to the concurrence of the delayed coincidence signal and the delayed energy verification pulses.
U.S. Pat. No. 4,476,386, issued Oct. 9, 1984, to Reid et al, discloses a method and apparatus for material analysis in which X-rays generated pursuant to incidence of an electron beam on the material are detected by a detector which generates signals representative of X-ray intensity. A first single analyzer is connected to receive the signals from the detector and to pass to an associated first counter a count signal whenever the signal applied to the first single channel analyzer is representative of an X-ray energy within a relatively narrow range of such energies. A second single channel analyzer is also connected to receive the signals from the detector and to pass to an associated second counter a count signal whenever the signal applied to the second analyzer is representative of an X-ray energy falling within a much broader range of such energies than the first mentioned range. The first and second counters accumulate the count signals applied thereto. The count in the second counter is compared by a comparator with a pre-established count in a third counter and when the count in the second counter assumes the same value as the count in the third counter the counts in the first and second counters are held. The so held count in the first counter then itself represents a normalized ratio of X-ray energy within the narrow range to the X-ray energy for the energy spectrum represented by the broad range of energies. On the basis of this normalized ratio information as to the makeup of the material can be derived.
U.S. Pat. No. 4,491,799, issued Jan. 1, 1985, to Giardinelli, discloses a device consisting essentially of a sampler device for sampling the baseline after every pulse processed in the spectroscopy amplifier, coupled to an averager circuit for averaging the samples, and to a LED display device, coupled to the average output and giving a visual indication of the value and sign of the averager output signal, the sampler and average circuits forming a so-called “boxcar integrator”, that is an essentially RC low-pass filter having a switch in series to the resistor.
U.S. Pat. No. 4,810,959, issued Mar. 7, 1989, to Padawer, discloses an invention that detects pulses, and, in response thereto, generates ramp functions with amplitudes corresponding to the interarrival times between successive pulses. These amplitudes are measured, and the occurrence of identical amplitudes are accumulated in corresponding memory locations, each of which has an address corresponding to a particular interarrival time. The resultant memory contents define a population distribution of interarrival times which is an exponential decay function of interarrival time. Interarrival times exceeding a preselected value are disregarded.
U.S. Pat. No. 4,870,603, issued Sep. 26, 1989, to Padawer, discloses an invention that detects pulses, and, in response thereto, generates ramp functions with amplitudes corresponding to the interarrival times between successive pulses. These amplitudes are measured, and the occurrence of identical amplitudes are accumulated in corresponding memory locations, each of which has an address corresponding to a particular interarrival time. The resultant memory contents define a population distribution of interarrival times which is an exponential decay function of interarrival time. Interarrival times exceeding a preselected value are disregarded.
U.S. Pat. No. 5,067,090, issued Nov. 19, 1991, to Seeman, discloses a nuclear spectroscopy method for pulse height analysis of an electrical signal emitted by a radiation detector and including nuclear events, such as pulses, whose amplitude is a measure of the energy of the gamma rays collected by said radiation detector, wherein (1) said signal is continuously converted to digital samples, at a given rate, and (2) each of the digital samples is processed so as to form a digital image of each detected pulse. The energy of each pulse is calculated by summing all sample values representative of this pulse and the sample just preceding the first sample representative of a pulse, as well as the sample just following the last sample representative of the same pulse.
U.S. Pat. No. 5,142,286, issued Aug. 25, 1992, to Ribner et al, discloses that sigma-delta analog-to-digital conversion is used in sensing apparatus that generates a digital signal descriptive of light energy received by a photosensor, such as one of a plurality of photosensors that together receive various elements of a radiant-energy image. A preamplifier generates an analog output signal responsive to the photocurrent of the photosensor, which analog output signal is undesirably accompanied by wideband noise. The analog output signal is supplied to a sigma-delta analog-to-digital converter, the decimation filter of which not only suppresses in the digital signal a component arising from the quantization noise from the sigma-delta modulator portion of the analog-to-digital converter, but also suppresses a component arising from remnant wideband noise from the preamplifier.
U.S. Pat. No. 5,347,129, issued Sep. 13, 1994, to Miller et al, discloses a radiation detection system that determines the type of nuclear radiation received in a detector by producing a correlation value representative of the statistical cross correlation between the shape of the detector signal and pulse shape data previously stored in memory and characteristic of respective types of radiation. The correlation value is indicative of the type of radiation. The energy of the radiation is determined from the detector signal and is used to produce a spectrum of radiation energies according to radiation type for indicating the nature of the material producing the radiation.
U.S. Pat. No. 5,493,122, issued Feb. 20, 1996, to Farr, discloses an energy-resolving x-ray detector for soft x-rays produced by elements having atomic numbers ranging from 9 to 23 includes a charge-coupled integrated circuit radiation detector device having an array of collection regions in a parallel plurality of collection shift registers forming columns of the array; an output amplifier for sequentially amplifying and signaling the charges received by the collection shift register; and a row shift register connected between the collection shift registers and the output amplifier; and a clock circuit having a multi-phase column output connected for sequentially shifting charges between collection regions of the collection shift register and into the row shift register during continuous exposure of the array to incoming radiation, each of the charges received by the output amplifier being sequentially accumulated in each of the collection regions of one collection shift register in response to the radiation, the clock circuit also having a multi-phase row output connected for sequentially shifting the charges from the row shift register to the output amplifier, the output amplifier having a reset connection to the clock circuit for momentarily resetting the input to the output amplifier at a predetermined level prior to receipt of each of the charges into the output amplifier. The output amplifier feeds an analog signal chain providing correlated double sampling. A spectrometer and thickness measurement apparatus suitable for monitoring silicone coatings includes the detector.
U.S. Pat. No. 5,574,284, issued Nov. 12, 1996, to Farr, discloses an energy-resolving x-ray detector for soft x-rays produced by elements having atomic numbers ranging from 9 to 23. The detector includes a charge-coupled integrated circuit radiation detector device having an array of collection regions in a parallel plurality of collection shift registers forming columns of the array; an output amplifier for sequentially amplifying and signaling the charges received by the collection shift register; and a row shift register connected between the collection shift registers and the output amplifier; and a clock circuit having a multi-phase column output connected for sequentially shifting charges between collection regions of the collection shift register and into the row shift register during continuous exposure of the array to incoming radiation, each of the charges received by the output amplifier being sequentially accumulated in each of the collection regions of one collection shift register in response to the radiation, the clock circuit also having a multi-phase row output connected for sequentially shifting the charges from the row shift register to the output amplifier, the output amplifier having a reset connection to the clock circuit for momentarily resetting the input to the output amplifier at a predetermined level prior to receipt of each of the charges into the output amplifier. The output amplifier feeds an analog signal chain providing correlated double sampling. A spectrometer and thickness measurement apparatus suitable for monitoring silicone coatings.
U.S. Pat. No. 5,684,850, issued Nov. 4, 1997, to Warburton et al, discloses a high speed, digitally based, signal processing system which accepts input data from a detector-preamplifier and produces a spectral analysis of the x-rays illuminating the detector. The system achieves high throughputs at low cost by dividing the required digital processing steps between a “hardwired” processor implemented in combinatorial digital logic, which detects the presence of the x-ray signals in the digitized data stream and extracts filtered estimates of their amplitudes, and a programmable digital signal processing computer, which refines the filtered amplitude estimates and bins them to produce the desired spectral analysis. One set of algorithms allow this hybrid system to match the resolution of analog systems while operating at much higher data rates. A second set of algorithms implemented in the processor allow the system to be self-calibrating as well. The same processor also handles the interface to an external control computer.
U.S. Pat. No. 5,873,054, issued Feb. 16, 1999, to Warburton et al, discloses a high speed, digitally based, signal processing system which accepts a digitized input signal and detects the presence of step-like pulses in the this data stream, extracts filtered estimates of their amplitudes, inspects for pulse pileup, and records input pulse rates and system lifetime. The system has two parallel processing channels: a slow channel, which filters the data stream with a long time constant trapezoidal filter for good energy resolution; and a fast channel which filters the data stream with a short time constant trapezoidal filter, detects pulses, inspects for pileups, and captures peak values from the slow channel for good events. The presence of a simple digital interface allows the system to be easily integrated with a digital processor to produce accurate spectra at high count rates and allow all spectrometer functions to be fully automated. Because the method is digitally based, it allows pulses to be binned based on time related values, as well as on their amplitudes, if desired.
U.S. Pat. No. 6,064,054, issued May 16, 2000, to Waczynski et al, discloses a radiation detector which includes a photoconductive detector and a modulator which modulates radiation passing to the photoconductive detector from a radiation source. An AC bias source is connected to the photoconductive detector and provides at least two levels of bias thereto. The modulator supplies synchronization signals to the AC bias source such that the level of bias supplied to the photoconductive detector is synchronized to the modulation of the radiation by the modulator. An integrator is connected to and receives an output signal generated by the photoconductive detector.
U.S. Pat. No. 6,222,175, issued Apr. 24, 2001, to Krymski, discloses a CMOS imager that includes an array of CMOS active pixel sensors and multiple column readout circuits each of which is associated with a respective column of sensors in the array and can perform correlated double sampling of values from a sensor in the respective column. Each column readout circuit also includes a crowbar switch which selectively can be enabled to force the stored values to an operational amplifier-based charge sensing circuit via a pair of buses. The operational amplifier-based charge sensing circuit, which includes a pair of switched integrators each of which is coupled to one of the buses, provides a differential output based on the values stored by a selected one of the column readout circuits.
U.S. Pat. No. 6,380,790, issued Apr. 30, 2002, to Denison, discloses an apparatus that includes a switching circuit, an integrator circuit having an input for receiving a first signal from the switching circuit, a sensing circuit having an input for receiving a second signal from the integrator circuit, and a control circuit having an input for receiving a third signal from the sensing circuit and an output for sending a fourth signal to the switching circuit. In certain applications, the integrator circuit includes a first integrator and a second integrator having an inverting terminal connected to an inverting terminal of the first integrator. The second integrator also includes a non-inverting terminal connected to an output of the first integrator through a first capacitor, and an output connected to a non-inverting terminal of the first integrator through a second capacitor.
U.S. Pat. No. 6,570,432, issued May 27, 2003, to Denison, discloses integrator circuit topologies that enable continuous integration without reset of the integrator circuit. One such integrator circuit includes a first integrator and a second integrator, each of the two integrators having a non-inverting terminal. Each of the non-inverting terminals is connected to an input node to alternately receive an input current for continuous integrator circuit integration without integrator circuit reset. The inverting terminal of the second integrator can be connected to an inverting terminal of the first integrator. The non-inverting terminal of the second integrator can be connected to an output of the first integrator through a first capacitor, and an output of the second integrator can be connected to a non-inverting terminal of the first integrator through a second capacitor. With such a capacitor connection, the capacitors alternately charge and discharge, based on integrator input current that is alternately directed between the non-inverting terminals of the integrators.
U.S. Pat. No. 6,609,075, issued Aug. 19, 2003, to Warburton et al, discloses techniques for measuring the baseline of the energy filter in nuclear and other spectrometers that filter pulses output by a preamplifier to measure the energy of events occurring in a detector connected to the preamplifier. These spectrometers capture the peak amplitudes of the filtered pulses as estimates of the underlying event energies and subtract a baseline value from these captured peak values in order to compensate for the energy filter's non-zero amplitude in the absence of any preamplifier output pulses. A second, baseline filter is connected to the preamplifier's output, where the basewidth of this baseline filter is significantly shorter than that of the energy filter. Times are determined when the baseline filter is not filtering preamplifier output pulses, output values from the baseline filter are captured during such determined times, and these baseline values captured from the baseline filter are used to create an accurate estimate of the energy filter's baseline value. Because the baseline filter's basewidth is much shorter than the energy filter's basewidth, large numbers of valid baseline filter values can be reliably captured at very high input count rates where it becomes difficult to capture baseline samples from the energy filter itself. It thus becomes possible to maintain the spectrometer's energy resolution and peak location stability to count rates four or more times higher than is possible without the method. The technique can be applied to both digital and analog spectrometers.
U.S. Pat. No. 6,653,636, issued Nov. 25, 2003, to Busse et al, and U.S. Patent Publication No. 2003/0146389, published Aug. 7, 2003, to Busse et al, discloses a sensor and a method of operating a sensor with includes a plurality of sensor elements (10), each of which includes a radiation-sensitive conversion element (1) which generates an electric signal in dependence on the incident radiation, and also with means (21 to 26) for amplifying the electric signal in each sensor element (10) and a read-out switching element (30) in each sensor element (10) which is connected to a read-out line (8) in order to read-out the electric signal. In order to provide a sensor in which a high stability of the transfer function and a favorable signal-to-noise ratio are ensured while maintaining a comparatively simple and economical construction, the means for amplifying include a respective source follower transistor (21) whose gate is connected to the conversion element (1), whose source is connected on the one side to an active load (23) and on the other side to one side of a sampling capacitor (26), the other side of the sampling capacitor (26) being connected to the read-out line (8) via the read-out switching element (30), a respective reset element (27) being connected to the conversion element (1) so as to reset the conversion element (1) to an initial state.
U.S. Pat. No. 6,703,959, issued Mar. 9, 2004, to Kuwabara, discloses a signal detecting method of repeating the processes of initiating accumulation of charge signals by switching an integrating amplifier to an accumulator mode, retaining a first electric signal outputted from the integrating amplifier immediately after switching to the accumulator mode, finding a difference as a signal component between a second electric signal outputted from the integrating amplifier immediately before switching to a reset mode after completing accumulation of the charge signals and the first electric signal, and converting and outputting the signal component into a digital signal. Here, the signal component concerning a first charge signal is retained by second signal retaining means and then converted into the digital signal. Further, the integrating amplifier is switched to the accumulator mode after completing accumulation concerning the first charge signal but before completing conversion into the digital signal to initiate accumulation concerning a second charge signal.
U.S. Pat. No. 6,917,041, issued Jul. 12, 2005, to Doty et al, discloses an event-driven X-ray CCD imager device that uses a floating-gate amplifier or other non-destructive readout device to non-destructively sense a charge level in a charge packet associated with a pixel. The output of the floating-gate amplifier is used to identify each pixel that has a charge level above a predetermined threshold. If the charge level is above a predetermined threshold the charge in the triggering charge packet and in the charge packets from neighboring pixels need to be measured accurately. A charge delay register is included in the event-driven X-ray CCD imager device to enable recovery of the charge packets from neighboring pixels for accurate measurement. When a charge packet reaches the end of the charge delay register, control logic either dumps the charge packet, or steers the charge packet to a charge FIFO to preserve it if the charge packet is determined to be a packet that needs accurate measurement. A floating-diffusion amplifier or other low-noise output stage device, which converts charge level to a voltage level with high precision, provides final measurement of the charge packets. The voltage level is eventually digitized by a high linearity ADC.
U.S. Patent Publication No. 2004/0026623, published Feb. 12, 2004, to Doty et al, discloses an event-driven X-ray CCD imager device that uses a floating-gate amplifier or other non-destructive readout device to non-destructively sense a charge level in a charge packet associated with a pixel. The output of the floating-gate amplifier is used to identify each pixel that has a charge level above a predetermined threshold. If the charge level is above a predetermined threshold the charge in the triggering charge packet and in the charge packets from neighboring pixels need to be measured accurately. A charge delay register is included in the event-driven X-ray CCD imager device to enable recovery of the charge packets from neighboring pixels for accurate measurement. When a charge packet reaches the end of the charge delay register, control logic either dumps the charge packet, or steers the charge packet to a charge FIFO to preserve it if the charge packet is determined to be a packet that needs accurate measurement. A floating-diffusion amplifier or other low-noise output stage device, which converts charge level to a voltage level with high precision, provides final measurement of the charge packets. The voltage level is eventually digitized by a high linearity ADC.
The related art disclosed above does not provide a single channel detector circuit that may be utilized with a wide variety of detectors and improve the response of existing detectors. Those skilled in the art have long sought and will appreciate the present invention that addresses these and other problems.